You should always give it a try for the status match. They were helpful in my case 2 times in the past for silver which at least gives you lounge access for your flights. Being SEN is already a good reason for them to match you, doesn't really cost them anything. Id say it's probably too late by now though since your flights are so soon.
Regarding your specific case with M&M be careful with the booking number and booking classes and make sure they actually earn something on M&M. There is a difference when you book with a M&M airline booking number or CX booking number as well. As suggested already, the best way is to add the frequent flyer number at a later stage when you already commenced your travel.
When I would be in such a situation, I would do the sorting out of these things upfront. Adding a FF number, when on travel, you no longer have the means to check out, whether your choice works out OK. Or maybe just claim afterwards, though it may give you less status during the travel and "maybe" missing experiences you would have appreciated.
As mxr mentioned, booking class can be completely different from the right to claim (and at which multiplier) to a FF program. Often the booking class does not earn anything on a foreign FF program, especially with these special code-share tickets. For example BA flight Z class legs (BA flight number, not a code-share), do not earn anything on MH Enrich, not even when the whole ticket is booked through MH. On the other hand CX does honour the miles/points on BA Z class....... All OneWorld, but little consistency.
Regarding the "costs" of the granted status, this can be considerable, when the visitor subsequently does use this status for lounge access on flights where the lounge owner does not earn a dime on the ticket (and subsequent flights).
Status match: Yeah, sometimes, though I don't think you would be granted anything, when you don't have not at least 2 LH returns booked on the "new" airline.
Or so to say, with just 1 upcoming code-share flight in CX metal, I have my doubts, if you would get anything more then maybe a "free" MPC account (you remember you have to pay USD 100 to even become an MPC member ?).